1. Field of the Invention
The invention relates to microphones, and more particularly to echo cancellation for signals generated by microphones.
2. Description of the Related Art
An audio processing device with full-duplex audio processing capability, such as a telephone, processes two signals transmitted in different directions. The audio processing device comprises two channels. One channel transmits a near-end signal comprising near-end voices to a far-end user, and the other channel transmits a far-end signal comprising far-end voices to a near-end user, thus enabling the near-end user and the far-end user to talk to each other.
Referring to FIG. 1, a block diagram of a portion of an audio processing device 100 with full-duplex audio processing capability is shown. The audio processing device 100 comprises a digital-to-analog converter 102, a speaker 104, a microphone 112, an analog-to-digital converter 114, and a digital signal processor 116. For a far-end channel, the digital-to-analog converter 102 first converts a far-end signal F1 from digital to analog to obtain a far-end signal F2. The speaker 104 then broadcasts the far-end signal F2 at the near-end side, enabling a near-end user to hear the far-end voices. For a near-end channel, the microphone 112 first converts a near-end sound comprising near-end voices to a near-end signal N1. The analog-to-digital converter 114 then converts the near-end signal N1 from analog to digital to obtain a near-end signal N2.
When the speaker 104 broadcasts the far-end signal F2, the microphone 112 converts a portion of the far-end voices sounded by the speaker 104 in addition to near-end voices to the near-end signal N1. The near-end signals N1 and N2 therefore comprise far-end voice components referred to as echoes. Thus, before the near-end signal N2 is transmitted to a far-end side, an echo component must be removed from the near-end signal N2. The digital signal processor 116 for echo cancellation comprises an adaptive filter 118 and a subtractor 120. The adaptive filter 118 first filters the far-end signal F1 to obtain a filtered far-end signal F3 comprising echo components. The subtractor 120 then subtracts the filtered far-end signal F3 from the near-end signal N2 to obtain a near-end signal N3 without echo components, thus completing echo cancellation.
The audio processing device 100, however, has deficiencies. First, the digital signal processor 116 for echo cancellation and the analog-to-digital converter 114 are separate elements, thus occupying a relatively larger layout area on a printed circuit board and increasing the size of the audio processing device 100. In addition, the audio processing device 100 cannot adjust a gain of the near-end signal N1. When amplitudes of near-end voices are low, a signal-to-noise ratio of the near-end signal N3 increases, degrading the quality of the near-end signal N3. When amplitudes of far-end voices broadcasted by the speaker 104 are high, the near-end signal N1 comprises an echo component with a high amplitude, thus saturating the analog-to-digital converter 114, and degrading the quality of the near-end signal N3. Thus, a microphone without the aforementioned deficiencies is therefore provided.